1. Field of the Invention
The present invention relates to a biodegradable tray for raising seedlings, which is used for raising plant seedlings or tissue culture. More precisely, it relates to a biodegradable tray for raising seedlings, which is composed of a pulp mold that is obtained by suction molding of pulp slurry.
2. Description of the Related Art
As trays, sheets or pots used for raising plant seedlings, plastic trays for raising seedlings are generally used. However, they suffer from the problem of disposal after use.
For example, there has been proposed a tray for raising seedlings which is obtained by lining up and arranging a suitable number of seedling housing units made of plastic having flexibility and elasticity in the longitudinal and transverse directions, connecting top peripheral edges of the openings of the adjacent seedling housing units, and providing dish-like parts downwardly protruding at the bottom of the seedling housing units, wherein the dish-like parts can freely protrude upwardly (Japanese Patent Laid-open (Kokai) No. 7-327507/1995). However, this tray for raising seedlings applies much load on the environment upon disposal because it uses plastic.
Therefore, trays consisting of pulp molds obtained by suction molding of pulp slurry have been developed. However, they suffer from problems of low strength and so forth.
Meanwhile, as a pulp mold having superior mechanical strength and good dimensional accuracy, there has been proposed a pulp mold produced by wet suction molding of pulp as a raw material, which comprises fine fibers having 150-500% of water retaining capacity defined in JAPAN TAPPI No. 26-78 (Japanese Patent Laid-open (Kokai) No. 10-311000/1998). Although use of this pulp mold is not particularly limited, it is to be mainly used as a packaging material, and use for tray for raising seedlings is not suggested.
Further, there has also been proposed a method for raising seedlings, wherein seedlings are raised in biodegradable cells placed in a conventionally used plastic tray (Japanese Patent Laid-open (Kokai) No. 10-225235/1998) and a product in which a thin film of non-biodegradable substance is formed on a surface of a biodegradable plastic article (Japanese Patent Laid-open (Kokai) No. 11-227110/1999). However, since they use a biodegradable plastic as a main component, they suffer from a problem that they must be expensive materials at present.
Furthermore, there has also been proposed a plastic mold composed of a mixture of 95-60 mass % of biodegradable plastic and 5-40 mass % of coconut shell (Japanese Patent Laid-open (Kokai) No. 10-67876/1998) and a biodegradable material obtained by kneading 51-70 mass % of biodegradable resin and 30-49 mass % of paper powder (Japanese Patent Laid-open (Kokai) No. 10-323810/1998). However, since they contain 30% or more of biodegradable plastic component, they also suffer from a problem that they must be expensive materials.
In reply to this situation, there has been proposed a biodegradable molded product obtained by heat adhesion of non-woven fabric consisting of a mixture of biodegradable fibers and cellulose fibers as a material, which can be produced at a relatively low cost (Japanese Patent Laid-open (Kokai) No. 9-272760/1997). However, since it mainly consists of a non-woven fabric, it is considered difficult to make it have a three-dimensional structure by molding.
The present invention was accomplished in view of the aforementioned problems, and its object is to provide a tray for raising seedlings, which is composed of a pulp mold that has superior dimensional accuracy, maintains its strength in use for a long period of time, is easily degraded after raising seedlings, and thus applies fewer loads on the environment.
The inventors of the present invention assiduously studied in order to achieve the aforementioned object. As a result, they found that mechanical strength and dimensional accuracy of a tray for raising seedlings, which is composed of a pulp mold, can be improved by subjecting the pulp mold for the tray to hot pressing after molding, and further found that the mechanical strength and dimensional accuracy can further be improved and the tray can be easily degraded after raising seedlings if a biodegradable resin is added to a pulp slurry for the tray. Thus, they accomplished the present invention.
That is, the present invention provides the followings.
(1) A biodegradable tray for raising seedlings, which is composed of a pulp mold obtained from pulp slurry containing a biodegradable resin by suction molding and hot pressing after the molding.
(2) The biodegradable tray for raising seedlings according to (1), wherein the biodegradable resin consists of one of resins selected from glycol-dicarboxylic acid polycondensates, polylactides and polylactones, which are aliphatic polyesters, or a mixture of two or more of them.
(3) The biodegradable tray for raising seedlings according to (1) or (2), wherein the content of the biodegradable resin is 25 mass % or less based on main material components.
(4) The biodegradable tray for raising seedlings according to any one of (1)-(3), wherein the pulp slurry contains an anitifungal agent.
(5) The biodegradable tray for raising seedlings according to any one of (1)-(4), wherein the pulp slurry contains a water-repellant and/or a waterproofing agent.